This invention relates to an improvement in an overlay of a sliding bearing, and more particularly to a sliding bearing material including an overlay having an excellent anti-seizure property suited for a high power design of an internal combustion engine used in an automobile, ship and industrial machinery.
Recently, internal combustion engines have increasingly had a high power design as well as a high speed design, and to meet this, an overlay has been formed by electroplating on a bearing alloy to improve surface properties such as conformability, embeddability and anti-seizure property. Recently, it has also been proposed to form an overlay by sputtering to enhance an anti-seizure property, wear resistance and corrosion resistance to thereby improve the performance of the bearing.
Examples of overlays formed by electroplating include a Pb-Sn alloy, a Pb-In-Sn alloy and a Pb-Sn-Cu alloy. These are a Pb alloy, and therefore are soft, and excellent in conformability, embeddability and anti-seizure property, but are inferior in fatigue resistance and wear resistance. Recently, internal combustion engines have been designed to produce an increased power for achieving a high performance and energy saving, and have had a compact design, so that the width of a bearing is reduced, and a bearing pressure acting on the bearing has become larger and larger. As a result, a conventional bearing has become unsuitable for the recent high power design of internal combustion engines. Furthermore, in the case of the electroplating, enormous costs have been required for disposing of waste liquids.
In order to solve the above problems, it has been proposed to form an overlay of an Al-20Sn alloy by sputtering to improve fatigue resistance, wear resistance and corrosion resistance; however, this overlay is high in hardness, and therefore is inferior in anti-seizure property.